Computer systems are typically accessed from terminals placed in user-convenient locations. In many computer applications, terminals are situated at remote locations. Oftentimes, these locations are scattered throughout a building or a plant site. It may even be desirable to access a host computer from different points in a city or from different cities. In all of these cases, a communication link is needed to transmit data between the host computer and the terminals. A standard communication link used for this purpose is a series of modems connected to a transmission line.
It is frequently desired to transmit independent system messages such as network management commands and responses for management of communication devices over data transmission lines without disturbing the existing data stream. These system messages may be either supporting a specific propriety network management protocol or they may be compatible with standard protocols.